Okay just for my understanding, for \$100, they will charge you 3% (=\$3) + \$2 so you are finally left with \$95? If that is the case I understood your question correct.

Let us assume you are at an ATM and click the "\$X" option. What you get is not \$X, but
$\$X \cdot(100\%-3\%)-\$2$ so you are left with $\$X\cdot0.97-\$2 $. If you actually want to have \$100 after they charged you, you want $\$X\cdot0.97-\$2 $ to equal \$100.

So you have to solve $\$X\cdot0.97-\$2 = \$100 $ for $\$X$. The results in
$$ \$X = \$102/0.97\approx \$105.15 $$